ABSTRACT
Photoacoustic imaging is emerging as a promising modality for small animal imaging in vivo by exploiting a new molecular contrast mechanism—optical absorption. This chapter demonstrates the feasibility of imaging gene expression by photoacoustic imaging for the first time. The concept of using reporter genes that modulate optical absorption as an image contrast mechanism represents a new paradigm for gene expression imaging. While the lacZ reporter gene system used presently shows the principle of gene expression imaging with photoacoustic technology, it has its limitations. Photoacoustic imaging has seen great success in small animal imaging during its short history in two distinct formats: photoacoustic tomography (PAT) and photoacoustic microscopy (PAM). A dual wavelength technique is used to image the targeted tumor after X-gal injection using PAM. Sensitivity analysis estimates that PAT is sensitive to micrometer-level concentrations of the blue product. The chapter measures the molar extinction spectrum of the blue product to determine an appropriate optical wavelength of illumination.
